Implantable medical devices, such as cardiac pacemakers, cardiac defibrillators, and neurostimulators, receive and/or deliver electrical signals to/from portions of the body via sensing and/or stimulating leads. Implantable medical devices typically include a metal housing (typically titanium) having a hermetically sealed interior space which isolates the internal circuitry, connections, power sources, and other device components from body fluids. A feedthrough device (often referred to simply as a feedthrough) establishes electrical connections between the hermetically sealed interior space and the exterior bodily fluid side of the device.
Feedthroughs typically include an insulator (typically ceramic) and electrical conductors or feedthrough pins which extend through the insulator to provide electrical pathways between the exterior and the hermetically sealed interior. A frame-like metal ferrule is disposed about a perimeter surface of the insulator, with the ferrule and insulator typically being joined to one another via a brazing or soldering process. The ferrule is configured to fit into a corresponding opening in the metal housing, with the ferrule being mechanically and hermetically attached to the housing, typically via laser welding. The insulator electrically insulates the feedthrough pins from one another and from the metal ferrule/housing.
The ferrule is typically joined to insulator via a welding or brazing process. However, the high temperatures employed by such processes heats the titanium of the housing about the perimeter of the opening to levels that cause a structural change in the titanium, commonly referred to as “grain growth”. This structural change can distort the dimensions of the opening and cause the titanium about the perimeter of the opening to become less rigid, each of which can result in a weaker joint between the ferrule and the housing.
Additionally, machining the ferrule (typically from pure titanium) to provide a high tolerance gap between the ferrule and the insulator (about 10-50 μm) which is necessary to achieve a quality braze joint is demanding and costly. Furthermore, if the gap is not maintained during the brazing process, or if the brazing process itself is not properly performed, a weak joint may be formed that can lead to premature failure of the implantable device.
For these and other reasons there is a need for the embodiments of the present disclosure.